Very informative thread. Thanks to all who've posted.
I can't speak to automotive kits but I do know that it was not unknown for vintage Aurora figure kits to be issued in different colours. I suspect, as Casey mentioned above that the different colours for the same issues were cases of running out of the main colour. Idle machines don't make money lol.
As for the black version shown on the original box, that could also have been a one off molded specifically for the photo shoot or one with a quick paint job for the same purpose.